Alpha plus beta type titanium alloy

ABSTRACT

A (α+β) type Ti alloy contains 7 wt % to 8.5 wt % of Al, 0.5 wt % to 1.5 wt % of V, 1 wt % to 3 wt % of Mo, 1 wt % to 3 wt % Cr, 0.3 wt % to 1 wt % of Fe, 0.05 wt % to 0.1 wt % of rare earth element, Ti, and unavoidable impurities. The Ti alloy can be produced by varmelting, forging, rolling and casting pressure processing or powder metallurgy. The total amount of impurities of C, H, O, and N is not higher than 0.25 wt %. V, Mo, and rare earth elements are added in forms of Al—V intermediate alloy, Al—Mo intermediate alloy, and La—Ce mixed rare earth, respectively. The room-temperature tensile strength and yield strength of the Ti alloy are higher than those of Ti—6Al—4V by more than 30%, the high-temperature strength is superior to that of Ti—6Al—4V, density and cost are lower than those of Ti—6Al—4V.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a titanium (Ti) alloy, and moreparticularly to a high-strength cost-effective Alpha plus Beta (α+β)type Ti alloy.

2. Related Art

(α+β) type Ti alloys are widely applied in the fields such as aviation,aerospace, automobile, golf club head, and bicycle, in which Ti—6Al—4Valloy successfully developed by U.S.A. in 1954 is a typicalrepresentative. Ti—6Al—4V alloy has preferable comprehensiveperformance, and present usage of Ti—6Al—4V alloy has been over a halfof all Ti alloys. However, the performance-to-price ratio of theTi—6Al—4V alloy is not high enough, long-term working temperature isaround 350° C., vanadium (V) of high content in the alloy makes theprice of the alloy relatively high, and the room-temperature strengthand high-temperature strength still have room to improve, which limitthe further application of Ti—6Al—4V alloy in national defense andmilitary industry and civilian products.

SUMMARY OF THE INVENTION

The present invention is directed to provide a high-strength (α+β) Tialloy, which has a higher performance-to-price ratio than that ofTi—6Al—4V and a long-term working temperature up to 450° C.

The technical solution of the present invention is as follows.

A (α+β) type Ti alloy contains 7 wt % to 8.5 wt % of Al, 0.5 wt % to 1.5wt % of V, 1 wt % to 3 wt % of Mo, 1 wt % to 3 wt % of Cr, 0.3 wt % to 1wt % of Fe, 0.05 wt % to 0.1 wt % of rare-earth elements, and the restare Ti and unavoidable impurities.

The Ti alloy of the present invention can be produced by general methodsof preparing Ti alloy, such as varmelting, forging, rolling, and castingprocessing or powder metallurgy. The total amount of impurities of C, H,O, and N is controlled to be not higher than 0.25 wt %. V is added inform of Al—V intermediate alloy, and Mo is added in form of Al—Mointermediate alloy, so as to ensure the accuracy and uniformity of theingredients of the alloy, thereby ensuring the consistency of theperformance of the alloy material. The rare earth elements are added inform of La—Ce mixed rare earth.

The Al content of the (α+β) type Ti alloy of the present invention ishigher than that of Ti—6Al—4V, and the increase of the Al content hassignificant effect in improving the room-temperature strength andhigh-temperature strength, reducing the specific gravity, and increasingthe elastic modulus. V, Mo, Cr, and Fe are β stabilizing elements.Compared with Ti—6Al—4V, the addition of V is significantly reduced,thus reducing the production cost of the Ti alloy. The addition ofproper amount of rare-earth elements improves the antioxidantperformance of the Ti alloy surface. The room-temperature tensilestrength and yield strength of the (α+β) Ti alloy of the presentinvention is improved by more than 30% compared with Ti—6 Al—4V,high-temperature strength is significantly superior to Ti—6 Al—4V,density and cost are a little lower than those of Ti—6 Al—4V. Therefore,the Ti alloy of the present invention has higher performance-to-priceratio than that of Ti—6 Al—4V, and has broad market prospects.

DETAILED DESCRIPTION OF THE INVENTION Embodiment 1

The Ti alloy of the present invention is manufactured by varmelting,forging, rolling and casting processing, the compositions of the alloyare formulated according to the alloy ingredients: 8.0 wt % of Al, 1.0wt % of V, 2.0 wt % of Mo, 2.0 wt % of Cr, 0.5 wt % of Fe, 0.08 wt % ofrare earth elements, and the rest of Ti and unavoidable impurities. Anelectrode composed of the alloy elements is melted in to an ingot by twotimes of vacuum consumable melting, and the melting vacuum is requiredto be lower than 1 Pa. During melting, V is added in form of Al—Vintermediate alloy, Mo is added in form of Al—Mo intermediate alloy,rare earth elements are added in form of La—Ce mixed rare earth, and theamount of the elements C, H, O, and N is strictly controlled to be nothigher than 0.25 wt %. The ingot is cogged and forged at 1000° C. to1200° C., and then further forged at a low temperature of 900° C. to1000° C., so as to get a plate block. Thereafter, the plate block is hotrolled at a temperature of 800° C. to 1000° C., and after annealingtreatment, a hot rolled Ti alloy plate is obtained.

The resultant Ti alloy plate (3 mm thick) is tested by National iron ofSteel Material Test Center, the room-temperature tensile strength is1270 MPa, the yield strength is 1200 MPa, elongation after fracture is10.0%, and the Rockwell hardness value is 42. The comprehensiveperformances at room temperature of the Ti alloy of the presentinvention and annealed Ti—6Al—4V alloy plate with the same thickness arecompared, and the results are listed in Table 1.

TABLE 1 Comparison of room-temperature performances of Ti alloy of thepresent invention and Ti—6Al—4V alloy Yield Tensile Rate of StrengthStrength Elongation Hardness Density Ti alloy Name (MPa) (MPa) (wt %)(HRC) (g/cm³) Ti—6Al—4V 870 925 ≧10 36 4.5 Ti alloy of the 1200 1270 1042 4.4 Present Invention

It can be seen from the data in the table that the density of the Tialloy of the present invention is a little lower than that of Ti—6Al—4V,the room-temperature strength is much superior to that of Ti—6Al—4V, thetensile strength and yield strength are improved by more than 30%compared with Ti—6Al—4V, and the plasticity is similar to that ofTi—6Al—4V. The Al content of the Ti alloy of the present invention ishigher than that of Ti—6Al—4V, but V content is much lower than that ofTi—6Al—4V, so the cost is lower than that of Ti—6Al—4V, and theperformance-to-price ratio is significantly higher than that ofTi—6Al—4V. Further, as the tensile strength at 440° C. of the resultantTi alloy plate of this embodiment is 960 MPa, and the tensile strengthat 400° C. of Ti—6Al—4V is 645 MPa, the high-temperature strength of theTi alloy of the present invention is significantly superior to that ofTi—6Al—4V.

1. An Alpha plus Beta (α+β) type titanium (Ti) alloy, comprising: 7 wt %to 8.5 wt % of Al, 0.5 wt % to 1.5 wt % of V, 1 wt % to 3 wt % of Mo, 1wt % to 3 wt % of Cr, 0.3 wt % to 1 wt % of Fe, 0.05 wt % to 0.1 wt % ofrare-earth elements, and the rest of Ti and unavoidable impurities. 2.The (α+β) type Ti alloy claimed as in claim 1, wherein total amount ofimpurities of C, H, O, and N is no higher than 0.25 wt %.
 3. An Alphaplus Beta (α+β) type titanium (Ti) alloy, comprising: 8.0 wt % of Al,1.0 wt % of V, 2.0 wt % of Mo, 2.0 wt % of Cr, 0.5 wt % of Fe, 0.08 wt %of rare-earth elements, and the rest of Ti and unavoidable impurities.4. The (α+β) type Ti alloy claimed as in claim 3, wherein the totalamount of impurities of C, H, O, and N is no higher than 0.25 wt %.